Up- and down-conversion, and multi-exciton generation for improving solar cells

A reality check

Hagay Shpaisman, Olivia Niitsoo, Igor Lubomirsky, David Cahen

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

Because conventional photovoltaic (PV) cells are threshold systems in terms of optical absorption, "photon management "is an obvious way to improve their performance. Calculations to optimize photon utilization in a single-junction PV cell show -1.4 eV to be the optimal bandgap for terrestrial solar to electrical power conversion. For Si, with a slightly sub-optimal gap, continuous efforts have yielded single-junction laboratory cells, quite close to the theoretical limit. One of the repeatedly proposed directions to improve photon management is that of up-and down-conversion of photon energy. In up-conversion two photons with energy hv <EG (the band gap) create one photon with hv > EG, while in down-conversion one photon with energy hv > 2EG, yields two photons with energy hv > EG. Multi-exciton generation (MEG), although not a "photon management" process, can achieve effects like down-conversion, which, though, is more limited than MEG. In MEG one photon with energy hv > HEG yields n electron-hole pairs with energy EG. Because MEG has clear advantages over down-conversion, in the following we will, instead of considering both, consider MEG. We find that a straightforward analysis of this approach to "photon management" for a single junction cell under the detailed balance limit shows clearly that, even if we assume (highly unrealistic) 100% efficient up-conversion and MEG, a new theoretical PV conversion limit of 49 %, instead of 31% is arrived at, a maximum possible gain of =60%. The main attractive feature of the combination of up-conversion and MEG is a significant broadening of the optimal band-gap range. Rough estimates for the very highest possibly feasible efficiencies for up-conversion and MEG (25% and 70% respectively), yield at most slightly less than 40% PV conversion efficiency, i.e., only a -25% gain over conventional single band gap semiconductor.

Original languageEnglish
Title of host publicationMaterials Research Society Symposium Proceedings
Pages133-142
Number of pages10
Volume1101
Publication statusPublished - 2008
EventLight Management in Photovoltaic Devices-Theory and Practice - San Francisco, CA, United States
Duration: Mar 24 2008Mar 28 2008

Other

OtherLight Management in Photovoltaic Devices-Theory and Practice
CountryUnited States
CitySan Francisco, CA
Period3/24/083/28/08

Fingerprint

Excitons
Solar cells
Photons
solar cells
excitons
photons
photovoltaic conversion
Energy gap
Photovoltaic cells
photovoltaic cells
energy
LDS 751
cells
Light absorption
Conversion efficiency
optical absorption
Semiconductor materials
thresholds
Electrons
estimates

ASJC Scopus subject areas

  • Materials Science(all)
  • Condensed Matter Physics
  • Mechanical Engineering
  • Mechanics of Materials

Cite this

Shpaisman, H., Niitsoo, O., Lubomirsky, I., & Cahen, D. (2008). Up- and down-conversion, and multi-exciton generation for improving solar cells: A reality check. In Materials Research Society Symposium Proceedings (Vol. 1101, pp. 133-142)

Up- and down-conversion, and multi-exciton generation for improving solar cells : A reality check. / Shpaisman, Hagay; Niitsoo, Olivia; Lubomirsky, Igor; Cahen, David.

Materials Research Society Symposium Proceedings. Vol. 1101 2008. p. 133-142.

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Shpaisman, H, Niitsoo, O, Lubomirsky, I & Cahen, D 2008, Up- and down-conversion, and multi-exciton generation for improving solar cells: A reality check. in Materials Research Society Symposium Proceedings. vol. 1101, pp. 133-142, Light Management in Photovoltaic Devices-Theory and Practice, San Francisco, CA, United States, 3/24/08.
Shpaisman H, Niitsoo O, Lubomirsky I, Cahen D. Up- and down-conversion, and multi-exciton generation for improving solar cells: A reality check. In Materials Research Society Symposium Proceedings. Vol. 1101. 2008. p. 133-142
Shpaisman, Hagay ; Niitsoo, Olivia ; Lubomirsky, Igor ; Cahen, David. / Up- and down-conversion, and multi-exciton generation for improving solar cells : A reality check. Materials Research Society Symposium Proceedings. Vol. 1101 2008. pp. 133-142
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